pg_sema.h File Reference

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Typedefs
typedef struct PGSemaphoreData *	PGSemaphore

Functions
Size	PGSemaphoreShmemSize (int maxSemas)
void	PGReserveSemaphores (int maxSemas)
PGSemaphore	PGSemaphoreCreate (void)
void	PGSemaphoreReset (PGSemaphore sema)
void	PGSemaphoreLock (PGSemaphore sema)
void	PGSemaphoreUnlock (PGSemaphore sema)
bool	PGSemaphoreTryLock (PGSemaphore sema)

Typedef Documentation

PGSemaphore

typedef struct PGSemaphoreData* PGSemaphore

Definition at line 34 of file pg_sema.h.

Function Documentation

PGReserveSemaphores()

void PGReserveSemaphores ( int  maxSemas )

extern

Definition at line 196 of file posix_sema.c.

{
    struct stat statbuf;
 
    /*
     * We use the data directory's inode number to seed the search for free
     * semaphore keys.  This minimizes the odds of collision with other
     * postmasters, while maximizing the odds that we will detect and clean up
     * semaphores left over from a crashed postmaster in our own directory.
     */
    if (stat(DataDir, &statbuf) < 0)
        ereport(FATAL,
                (errcode_for_file_access(),
                 errmsg("could not stat data directory \"%s\": %m",
                        DataDir)));
 
#ifdef USE_NAMED_POSIX_SEMAPHORES
    mySemPointers = (sem_t **) malloc(maxSemas * sizeof(sem_t *));
    if (mySemPointers == NULL)
        elog(PANIC, "out of memory");
#else
 
    sharedSemas = (PGSemaphore)
        ShmemAlloc(PGSemaphoreShmemSize(maxSemas));
#endif
 
    numSems = 0;
    maxSems = maxSemas;
    nextSemKey = statbuf.st_ino;
 
    on_shmem_exit(ReleaseSemaphores, 0);
}

References DataDir, elog, ereport, errcode_for_file_access(), errmsg(), FATAL, fb(), malloc, maxSemaSets, maxSems, maxSems, maxSharedSemas, mySemaSets, mySemSet, nextSemaKey, nextSemaNumber, nextSemKey, numSemaSets, numSems, numSems, numSharedSemas, on_shmem_exit(), PANIC, PGSemaphoreShmemSize(), ReleaseSemaphores(), ReleaseSemaphores(), ReleaseSemaphores(), SEMAS_PER_SET, sharedSemas, sharedSemas, ShmemAlloc(), and stat.

Referenced by InitProcGlobal().

PGSemaphoreCreate()

PGSemaphore PGSemaphoreCreate ( void  )

extern

Definition at line 257 of file posix_sema.c.

{
    PGSemaphore sema;
    sem_t      *newsem;
 
    /* Can't do this in a backend, because static state is postmaster's */
    Assert(!IsUnderPostmaster);
 
    if (numSems >= maxSems)
        elog(PANIC, "too many semaphores created");
 
#ifdef USE_NAMED_POSIX_SEMAPHORES
    newsem = PosixSemaphoreCreate();
    /* Remember new sema for ReleaseSemaphores */
    mySemPointers[numSems] = newsem;
    sema = (PGSemaphore) newsem;
#else
    sema = &sharedSemas[numSems];
    newsem = PG_SEM_REF(sema);
    PosixSemaphoreCreate(newsem);
#endif
 
    numSems++;
 
    return sema;
}

References Assert, elog, ereport, errmsg(), fb(), IpcSemaphoreCreate(), IpcSemaphoreInitialize(), IsUnderPostmaster, maxSemaSets, maxSems, maxSems, maxSharedSemas, mySemaSets, mySemSet, nextSemaNumber, numSemaSets, numSems, numSems, numSharedSemas, PANIC, PG_SEM_REF, PosixSemaphoreCreate(), SEMAS_PER_SET, PGSemaphoreData::semId, PGSemaphoreData::semNum, sharedSemas, and sharedSemas.

Referenced by InitProcGlobal().

PGSemaphoreLock()

void PGSemaphoreLock ( PGSemaphore  sema )

extern

Definition at line 315 of file posix_sema.c.

{
    int         errStatus;
 
    /* See notes in sysv_sema.c's implementation of PGSemaphoreLock. */
    do
    {
        errStatus = sem_wait(PG_SEM_REF(sema));
    } while (errStatus < 0 && errno == EINTR);
 
    if (errStatus < 0)
        elog(FATAL, "sem_wait failed: %m");
}

References CHECK_FOR_INTERRUPTS, EINTR, elog, ereport, errmsg(), FATAL, fb(), PG_SEM_REF, pgwin32_dispatch_queued_signals(), pgwin32_signal_event, PGSemaphoreData::semId, and PGSemaphoreData::semNum.

Referenced by BufferLockAcquire(), BufferLockDequeueSelf(), LWLockAcquire(), LWLockAcquireOrWait(), LWLockDequeueSelf(), LWLockWaitForVar(), ProcArrayGroupClearXid(), and TransactionGroupUpdateXidStatus().

PGSemaphoreReset()

void PGSemaphoreReset ( PGSemaphore  sema )

extern

Definition at line 290 of file posix_sema.c.

{
    /*
     * There's no direct API for this in POSIX, so we have to ratchet the
     * semaphore down to 0 with repeated trywait's.
     */
    for (;;)
    {
        if (sem_trywait(PG_SEM_REF(sema)) < 0)
        {
            if (errno == EAGAIN || errno == EDEADLK)
                break;          /* got it down to 0 */
            if (errno == EINTR)
                continue;       /* can this happen? */
            elog(FATAL, "sem_trywait failed: %m");
        }
    }
}

References EAGAIN, EINTR, elog, FATAL, fb(), IpcSemaphoreInitialize(), PG_SEM_REF, PGSemaphoreTryLock(), PGSemaphoreData::semId, and PGSemaphoreData::semNum.

Referenced by InitAuxiliaryProcess(), and InitProcess().

PGSemaphoreShmemSize()

Size PGSemaphoreShmemSize ( int  maxSemas )

extern

Definition at line 165 of file posix_sema.c.

{
#ifdef USE_NAMED_POSIX_SEMAPHORES
    /* No shared memory needed in this case */
    return 0;
#else
    /* Need a PGSemaphoreData per semaphore */
    return mul_size(maxSemas, sizeof(PGSemaphoreData));
#endif
}

References fb(), and mul_size().

Referenced by PGReserveSemaphores(), and ProcGlobalShmemSize().

PGSemaphoreTryLock()

bool PGSemaphoreTryLock ( PGSemaphore  sema )

extern

Definition at line 360 of file posix_sema.c.

{
    int         errStatus;
 
    /*
     * Note: if errStatus is -1 and errno == EINTR then it means we returned
     * from the operation prematurely because we were sent a signal.  So we
     * try and lock the semaphore again.
     */
    do
    {
        errStatus = sem_trywait(PG_SEM_REF(sema));
    } while (errStatus < 0 && errno == EINTR);
 
    if (errStatus < 0)
    {
        if (errno == EAGAIN || errno == EDEADLK)
            return false;       /* failed to lock it */
        /* Otherwise we got trouble */
        elog(FATAL, "sem_trywait failed: %m");
    }
 
    return true;
}

References EAGAIN, EINTR, elog, ereport, errmsg(), EWOULDBLOCK, FATAL, fb(), IPC_NOWAIT, PG_SEM_REF, PGSemaphoreData::semId, and PGSemaphoreData::semNum.

Referenced by PGSemaphoreReset().

PGSemaphoreUnlock()

void PGSemaphoreUnlock ( PGSemaphore  sema )

extern

Definition at line 335 of file posix_sema.c.

{
    int         errStatus;
 
    /*
     * Note: if errStatus is -1 and errno == EINTR then it means we returned
     * from the operation prematurely because we were sent a signal.  So we
     * try and unlock the semaphore again. Not clear this can really happen,
     * but might as well cope.
     */
    do
    {
        errStatus = sem_post(PG_SEM_REF(sema));
    } while (errStatus < 0 && errno == EINTR);
 
    if (errStatus < 0)
        elog(FATAL, "sem_post failed: %m");
}

References EINTR, elog, ereport, errmsg(), FATAL, fb(), PG_SEM_REF, PGSemaphoreData::semId, and PGSemaphoreData::semNum.

Referenced by BufferLockAcquire(), BufferLockDequeueSelf(), BufferLockWakeup(), IpcSemaphoreCreate(), LWLockAcquire(), LWLockAcquireOrWait(), LWLockDequeueSelf(), LWLockUpdateVar(), LWLockWaitForVar(), LWLockWakeup(), ProcArrayGroupClearXid(), and TransactionGroupUpdateXidStatus().